1. Field of the Invention
This invention relates generally to a diffusion apparatus, a chemical vapor deposition (CVD) apparatus or a like apparatus for processing a semiconductor wafer, and more particularly to a supplying method and a supplying apparatus wherein works are supplied in a batch to a batch process apparatus so as to be processed in a batch by the batch process apparatus.
2. Description of the Related Art
In a semiconductor wafer process, an operation of forming works such as wafers into a batch is conventionally performed by an operator. In particular, from within a plurality of works transported to the batch process apparatus, those of the works for which processing conditions are the same are selected by the operator, and a predetermined number of such works are put in order and formed into a batch and then supplied to the batch process apparatus by the operator. The conventional work supplying method just described has such problems as described below. In particular, since selection of works to be formed into a batch is performed based on a determination by an operator in this manner, there is the possibility that the wrong determination may be made, and in this instance, unacceptable goods processed by a process different from a required process are produced. Further, the operator has a heavy responsibility in that the operator must form works into a batch after a preferential order of the works is recognized. The presence of the operator presents an undesirable labor intensive impediment. In addition, as the size of wafers to be handled increases, the number of works which can be prepared for a production line decreases, and as a result, the batch process apparatus fails in formation of a batch from a predetermined number of works. Even if the operation rate of the apparatus achieves the desired rate, a desired processing quantity cannot be achieved, and the stacking quantity decreases.
In order to eliminate the problems of the conventional work supplying method described above, a batch supplying method which exhibits an improved batch efficiency and allows automation of operation has been proposed in Japanese Patent Laid-Open Application No. Heisei 3-236213.
In particular, according to the batch supplying method disclosed in the document mentioned above, a formation number of works to be formed into a batch is decided and feeding situations, processing conditions, processing times and a preferential order for processing of different works are determined in advance. Those works which have the same processing conditions are arranged in a descending order of the preferential degree. Then, if the number of works equal to the formation number are on hand, they are formed as they are into a batch to be supplied. Otherwise if the number of works equal to the formation number is not on hand, then it is determined based on arrival times, processing times and a preferential order of works predicted depending upon the feeding situations whether or not one should be waited for all of the works to arrive to form one batch. Based on a result of this determination, a batch to be supplied to the batch process apparatus is formed from works of a number either equal to or smaller than the formation number.
The conventional batch supplying method described above, however, has problems as described below.
In particular, the first problem resides in that it sometimes occurs that those works whose delivery date is critical, that is, those works which have a comparatively higher preferential degree or degrees, are processed not preferentially but after processing of other works, resulting in failure in delivery of products on or prior to the delivery date.
The reason is that, when the number of works equal to the predetermined formation number are already prepared for the batch process apparatus, the works of the higher preferential degree are left without being supplied till the next timing for formation of a batch. This is because a batch is formed only from the works currently prepared for the batch process apparatus, even if works having a higher preferential degree or degrees than the works prepared in the batch are prepared for the batch process apparatus before the prepared works are actually processed by the batch process apparatus.
The second problem to be solved regarding the conventional batch supplying method described above resides in that, if works formed into a batch are processed as they are by the batch process apparatus, then there is the possibility that unacceptable products may be produced from the works.
The reason is that, although, when a number of works equal to the formation number are not on hand, an arrival time of a work is predicted and it is determined whether or not formation of a batch should waite till such arrival time. If the formation should waite till the arrival time, such determination is made without taking into consideration whether or not a time limitation between different steps is present, and if the presence of such time limitation is not taken into consideration, then unacceptable products may possibly be produced.